| Abstract |
Thiol protease inhibitors (TPIs) were isolated from culture media and cell
extracts of two human lung cancer cell lines and were characterized by
biochemical and biological means to understand the relationship between
cancer growth and TPI. 1) High molecular weight (HMW-) TPI and low
molecular weight (LMW-) TPI were purified from culture media of human lung
cancer cell line LK-2 (squamous cell carcinoma) by gel filtlation on
Sephadex G-100 and ion exchange chromatography on DEAE-Sephacel. Their
molecular weight (MW) were estimated to be 90,000 and 10,000,
respectively, by gel filtlation. LMW-TPI was dominant in TPI activity.
LMW-TPI is stable below 60 Celsius and in a range of pH 6-10. LMW-TPI was a
specific inhibitor of thiol protease. From LK-2 cell extract, only LMW-TPI
(MW 10,000) could be detected. 2) None of TPIs, purified from culture
media or cells of LK-2, reacted with anti-UTPI rabbit IgG or anti-alpha2-TPI
rabbit IgG by double immunodiffusion method. 3) From a human lung
adenocarcinoma cell line, luci-10, both HMW-TPI and LMW-TPI were purified
from culture media but only LMW-TPI from cell extracts. 4) Daily
examination of TPI activity in culture media of Luci-10 showed that cancer
cells at stationary phase released TPI two to three times more than at
logarithmic growth phase. 5) LMW-TPI, purified from culture media of LK-2,
suppressed incorporation of 3H-Thymidine of LK-2 cells. Other TPIs
(alpha2-TPI in serum, UTPI in urine, a microbial protease inhibitor E64)
suppressed it. On the other hand, Serine protease inhibitors such as UTI
in urine and soybean trypsin inhibitor had no effect. 6) Thiol proteases
such as papain, ficin, and cathepsin B stimulated incorporation of
3H-Thymidine of LK-2 cells.
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